FIG. 5(a) is a plan view showing a pixel region of an active matrix substrate incorporated in a conventional liquid crystal display device. As shown in FIG. 5(a), the active matrix substrate has a plurality of pixel electrodes 54 provided in a matrix form. Gate wirings 51 and source wirings 52 are provided around the pixel electrodes 54 so as to orthogonally cross each other. A TFT 53 is provided in neighborhoods of crossing points of the gate and source wirings 51 and 52 as a switching element connected to the pixel electrode 54 through a contact hole.
FIG. 5(b) is a cross-sectional view taken along line B--B of the active matrix substrate incorporated in the liquid crystal display device shown in FIG. 5(a). As shown in FIG. 5(b), a gate electrode 61 branching off from the gate wiring 51 shown in FIG. 5(a) is provided on a transparent insulating substrate 60. A gate insulating film 55 is provided to cover the gate electrode 61. A semiconductor layer 64 is provided on the gate insulating film 55 above the gate electrode 61. A channel protection layer 65 is provided on the center of the semiconductor layer 64. Two n.sup.30 layers 66, respectively serving as a source area and a drain area, are provided so as to cover both ends of the semiconductor layer 64 and the channel protection layer 65, and to be separated from each other on the channel protection layer 65. The n.sup.+ layers 66 are connected respectively to the source electrode 62 branching off from the source wiring 52 and the drain electrode 63. An interlayer insulating film 59 is provided to cover the TFT 53 and the gate and source wirings 51 and 52 provided in this manner. The pixel electrode 54 is provided on the interlayer insulating film 59. The pixel electrode 54 is connected to the drain electrode 63 of the TFT 53 through the contact hole in the interlayer insulating film 59.
Finally, the manufacturing process of the conventional liquid crystal display device becomes complete with sealing liquid crystal 58 between a TFT substrate 70 configured in the above manner and an opposite substrate 71 equipped with an opposite electrode 56. Here, spacers 57 are sandwiched between the TFT substrate 70 and the opposite substrate 71 to maintain a predetermined space therebetween (disclosed in Japanese Laid-Open Patent Application No. 61-156025/1986 Tokukaishou 61-156025).
Polyimide resin is used as the interlayer insulating film 59 in the conventional liquid crystal display device disclosed in the above laid-open patent application. However, other highly transparent materials, such as acrylic resin, polystyrene and polyester, are also generally used.
Although no disclosure is made about the spacers 57, plastic beads and hard materials, such as glass, are usually used. The plastic bead spacer is generally made of polyimide, epoxy and polystyrene.
Nevertheless, if the above-mentioned acrylic resin is used as the interlayer insulating film 59 and the spacers 57 are made using epoxy resin, Newton rings are observed in a lighting test after injecting and sealing the liquid crystal (Newton rings are a series of circular bright and dark bands, which look like a wave pattern created on water surface by a stone dropping into the water). Especially the phenomenon frequently occurs in the sealing portion, and the rings were even more clearly observed with a liquid crystal display device incorporating an interlayer insulating film in an underlayer of the sealing portion. Consequently, such a liquid crystal display device has problems of a high defective ratio and low reliability.